In the field of laser amplification devices having a solid-state lasing medium, until recently there existed two broad types of amplifying materials:                firstly, single-crystal materials, for example yttrium aluminum garnet (also called YAG), sapphire or ruby. These materials are generally doped, for example with rare-earth ions or with titanium or chromium;        secondly, amorphous matrices, such as phosphate glass for example or silicate glass. These matrices are mainly doped with rare-earth ions.        
In general, amplification devices with a single-crystal amplifying medium, of the YAG matrix type for example, make it possible to achieve high repetition rates but at modest beam energies. This energy limitation is due to the limited cross section of single-crystal amplifying media, said limitation being set by the crystal growing process. For example, the difficulty of growing single-crystal neodymium-doped YAG, referred to as Nd:YAG, over large cross sections and the limitation of its damage threshold make it possible at best to obtain energies of around 4 to 5 joules for a 2 cm2 cross section, in pulsed mode with a laser pulse duration of a few nanoseconds.
Moreover, amplification devices comprising a glass amplifying medium can achieve high beam energies, ranging from around ten joules to several kilojoules, but at respective rates ranging from one Hz to less than one laser shot per hour. The high energies are permitted thanks to the large possible cross sections of such an amplifying medium. There is no limitation on the cross section in the case of glass matrices, unlike in single crystals. However, glass matrices, because of their poor thermomechanical properties, prevent the laser rates from being increased and sometimes require, notably, the use of complex means of compensating for wavefront distortion.
The main techniques for optically pumping solid-state amplifying media comprise, on the one hand, continuous lamp or flashlamp pumping and, on the other hand, continuous or pulsed laser diode pumping.
The main characteristics of each of these optical pumping techniques are the following:                continuous lamps emit a multi-line spectrum superimposed on quite a low continuum;        flashlamps emit a spectrum essentially consisting of a continuum on which low-intensity spectral lines are superposed. The spectral position of the emission lines depends on the gas or gases used in the lamp; and        laser diodes emit a single spectral line, which depends on the semiconductor used.        
When a lasing material is pumped by one of these techniques, it becomes an amplifier for one or more characteristic wavelengths.
Each of these two pumping techniques has advantages and disadvantages, the main ones of which are the following:                when a lasing material is lamp-pumped, only a small part of the emission spectrum of the lamp is useful for pumping, the other part being partially thermally dissipated in the lasing medium. This thermal dissipation, if it becomes too high, may induce distortions of the wavefront and/or birefringence limiting possible applications of the laser;        the lifetime of the continuous lamps and flashlamps is often much shorter than that of continuous diodes and pulsed diodes respectively. As a result, maintenance operations on lamp-pumped lasers are carried out more frequently;        
for the same performance, the cost of lamp-pumped amplifiers is much lower than that of diode-pumped amplifiers;
for a number of lasing materials, there are pump diodes that emit at a wavelength coinciding with one of their absorption lines. Consequently, the thermal dissipation in the amplifying medium is reduced and the induced deleterious effects (wavefront distortion, induced birefringence, etc.) are reduced. Thus, with continuous pumping it is possible to obtain a higher average power output by the laser if it is diode-pumped rather than lamp-pumped. Furthermore, with pulsed pumping, the same output laser energies are obtained irrespective of the type of pump (flashlamp or diode), but higher repetition rates may be achieved with diode pumping; and                the cost of diodes is much higher than that of lamps, and therefore the cost of maintaining them under operational conditions may be higher than that for a lamp-pumped laser.        
Thus, notably in the field of pulsed lasers, it is possible at the present time to manufacture:                solid-state laser amplifiers delivering high energies, of the type comprising glass-based lasing materials, but at very low repetition rates because of the thermal effects if they are flashlamp-pumped;        solid-state laser amplifiers delivering high energies, of the type comprising glass-based lasing materials, but at low repetition rates because of the thermal effects and at very high costs if they are diode-pumped;        flashlamp-pumped solid-state laser amplifiers operating at intermediate repetition rates, of the order of 10 to 100 Hz, thanks to the use of certain single-crystal lasing materials having good thermomechanical properties, but delivering energies limited to a few joules owing to the limited cross section of the crystals that can be achieved by crystal growth; and        expensive diode-pumped solid-state laser amplifiers operating at high repetition rates, at more than 50 Hz, thanks to the use of certain single-crystal lasing materials having good thermomechanical properties but delivering energies limited to a few joules owing to the limited cross section of the crystals that can be obtained by crystal growth.        
The appearance of new lasing materials that combine the advantages of glass matrices, having large available cross sections enabling high energies to be achieved, with those of the best single-crystal materials having good thermomechanical properties, opens up new prospects.
These new lasing materials are polycrystalline solid-state structures, also called laser ceramics.
It is now possible to produce laser amplifier devices delivering at the same time high energies at intermediate repetition rates in the case of flashlamp pumping, or high repetition rates in the case of diode pumping.
The choice of pumping technique is therefore mainly guided by purchase cost and maintenance cost considerations. To pump amplifying medium volumes possibly in excess of 200 cm3, compared to about 20 cm3 previously, the acquisition cost of a diode-pumped amplification device may be high. Therefore lamp pumping becomes a worthwhile alternative for industrial manufacturers.
For example, a YAG ceramic doped with Nd3+ rare-earth ions, owing to its polycrystalline structure that allows large amplifying media to be obtained, having a cross section exceeding 20 cm2 with an Nd:YAG single crystal, may be employed for producing high-energy amplification devices. These energies obtained are around several tens of joules, thus exceeding the 4 to 5 joules usually obtained. The rates achieved greatly exceed 10 Hz.
However, there are certain problems when pumping laser ceramics by lamps. Part of the emission spectrum of the lamps lies within the ultraviolet. This radiation can damage laser ceramics as it induces a solarization effect which ultimately degrades the optical properties of the laser ceramic used as amplifying medium. Consequently, when designing laser amplification devices using laser ceramics, it is necessary to employ techniques that prevent the laser ceramic from being degraded by the ultraviolet radiation of the lamps.
It is conceivable with these laser ceramics to produce new lasers that can deliver high average power levels with a much lower average cost per watt than with the complex solutions currently used, of the type in which the number of lasers is increased or the beams are multiplexed together.